Phase diagrams,melt solidification and glass crystallization in the Bi-Ca-Sr-Cu-(O) system

Some aspects of the preparation of oxide superconductors are discussed as concerns the problems of weak links. Known binary phase diagrams are reviewed and redrawn. Ternary compounds and glass-formation regions are included. The crystallization and formation of superconducting phases are illustrated by means ofT-T-T diagrams. The rate-controlling process of polymorphous precipitation is probably two-dimensional nucleation.

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Zusammenfassung Es wurden einige Aspekte der Herstellung von Oxidsupraleitern bezüglich der Probleme schwacher Bindungen besprochen. Existierende binÄre Phasendiagramme wurden kritisch besprochen und unter Berücksichtigung von ternÄren Verbindungen und Glasbildungen neu erstellt. Die Kristallisierung und Bildung von supraleitenden Phasen wurde mittels T-T-T-Diagrammen illustriert. Der geschwindigkeitsbestimmende Schritt der polymorphen PrÄzipitation ist wahrscheinlich eine zweidimensionale Kristallkeimbildung.

     

The gas-phase equilibrium structures of Si8O12(OSiMe3)8 and Si8O12(CHCH2)8

The equilibrium molecular structure of Si(8)O(12)(OSiMe(3))(8) has been determined in the gas phase by electron diffraction (GED). With OSi-containing substituents on the cage silicon atoms, this molecule contains a moiety, which would, if reproduced in a periodic manner, yield a zeolite-type structure. Extensive ab initio calculations were used to identify two conformers of this molecule, with D(4) and D(2) point-group symmetries; the D(4)-symmetric conformer was approximately 1.2 kJ mol(-1) lower in energy. With 132 atoms in each conformer, this is one of the largest studies to be undertaken using gas electron diffraction. Semiempirical molecular-dynamics (SE-MD) calculations were used to give amplitudes of vibration, vibrational distance corrections (differences between interatomic distances in the equilibrium structure and the vibrationally averaged distances that are given directly by the diffraction data), and anharmonic constants. The structure of Si(8)O(12)(CHCH(2))(8) has also been determined by GED. Calculations showed that the vinyl groups are fairly unhindered and rotate between three minimum-energy positions. Ultimately, all possible combinations of the vinyl groups in these low-energy positions were accounted for in the GED model.     

Preparation and reactivity of [D3d]-octahedrane: the most stable (CH)12 hydrocarbon

The synthesis of the (CH)12 hydrocarbon [D(3d)]-octahedrane (heptacyclo[6.4.0.0(2,4).0(3,7).0(5,12).0(6,10).0(9,11)]dodecane) 1 and its selective functionalization retaining the hydrocarbon cage is described. The B3LYP/6-311+G* strain energy of 1 is 83.7 kcal mol(-1) (4.7 kcal mol(-1) per C-C bond) which is significantly higher than that of the structurally related (CH)16 [D(4d)]-decahedrane 2 (75.4 kcal mol(-1); 3.1 kcal mol(-1) per C-C bond) and (CH)20 [I(h)]-dodecahedrane 3 (51.5 kcal mol(-1); 1.7 kcal mol(-1) per C-C bond); the heats of formation for 1-3 computed according to homodesmotic equations are 52, 35, and 4 kcal mol(-1). Catalytic hydrogenation of 1 leads to consecutive opening of the two cyclopropane rings to give C2-bisseco-octahedrane (pentacyclo[6.4.0.0(2,6).0(3,11).0(4,9)]dodecane) 16 as the major product. Although 1 is highly strained, its carbon skeleton is kinetically quite stable: Upon heating, 1 does not decompose until above 180 degrees C. The B3LYP/6-31G* barriers for the S(R)2 attack of the tBuO. and Br3C. radicals on a carbon atom of one of the cyclopropane fragments (Delta(298) = 27-28 kcal mol(-1)) are higher than those for hydrogen atom abstraction. The latter barriers are virtually identical for the abstraction from the C1-H and C2-H positions with the tBuO. radical (DeltaG(298) = 17.4 and 17.9 kcal mol(-1), respectively), but significantly different for the reaction at these positions with the Br3C. radical (DeltaG(298) = 18.8 and 21.0 kcal mol(-1)). These computational results agree well with experiments, in which the chlorination of 1 with tert-butyl hypochlorite gave a mixture of 1- and 2-chlorooctahedranes (ratio 3:2). The bromination with carbon tetrabromide under phase-transfer catalytic (PTC) conditions (nBu4NBr/NaOH) selectively gave 1-bromooctahedrane in 43 % isolated yield. For comparison, the PTC bromination was also applied to 2,4-dehydroadamantane yielding 54 % 7-bromo-2,4-dehydroadamantane.     

On the interaction of O(1S) with O(3P)

The quenching rate for O(¹S) by O(³P) into the O(¹D) + O(¹D) channel is calculated using a theoretically calculated spin-orbit coupling matrix element. An upper bound to the rate is found to be 2.0 × 10^?14 cm³ s^?1 which is much smaller than the experimental value. The low value of the rate constant is the result of a spin-orbit coupling matrix element of about 3 cm^?1 at the relevant curve corssing.     

Zur Kristallchemie der Kupfer-Lanthanoid-Oxowolframate: (I) triklin-α-CuTbW2O8, (II) monoklin-CuInW2O8 und (III) monoklin-CuYW2O8

The Crystal Chemistry of Copper Rare-Earth Oxotungstates: (I): triclinic-α-CuTbW₂O₈, (II): monoclinic-CuInW₂O₈ and (III): monoclinic-CuYW₂O₈ Single crystals of (I), (II) and (III) were prepared by recrystallisation in closed systems and examined by X-ray technique. (I): space group C? P1 , a = 7.3080, b = 7.8945, c = 7.1476 Å, α = 115.23, β = 116.21, γ = 56.98°, Z = 2; (II): space group C? C2/c, a = 9.6576, b = 11.6496, c = 4.9863 Å, β = 91.17°, Z = 4; (III): space group C? P2/n, a = 10.0504, b = 5.8214, c = 5.0224 Å, β = 94.23°, Z = 2. The crystal structures are discussed with respect to calculations of the coulombterms of lattice energy and possible valence states of Cu²⁺ and Mo⁵⁺.     

Phase equilibrium in the system Na5P3O10-Na8La2(PO3)8O3

The phase diagram Na₈La₂(PO₃)₈O₃-Na₅P₃O₁₀, which comprises part of the ternary system La₂O₃-Na₂O-P₂O₅, was constructed in the laboratory. The oxyphosphate Na₈La₂(PO₃)₈O₃ crystallizes in the orthorombic system; the lattice parameters are as follows a=8.96(4)Å, b=9.35(8)Å, c=12.29(7)Å.

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Zusammenfassung Es wurde das Phasendiagramm Na₈La₂(PO₃)₈O₃ - Na₅P₃O₁₀, welches einen Teil des ternären Systemes La₂O₃ - Na₂O - P₂O₅ enthält, konstruiert. Das Oxyphosphat Na₈La₂(PO₃)₈O₃ kristallisiert rhombisch mit folgenden Gitterkonstanten: a=8.96(4)Å, b=9.35(8)Å, c=12.29(7)Å.

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The author thanks Mrs. E. Dlugoszewska for technical assistance.     

Rough-surface crystallization: Some applications to poly(ethylene oxide)

A model incorporating a rough (disordered) crystal growth surface is capable of treating many of the observations and measurements on the crystal growth of short chains of poly(ethylene oxide) from the melt. A simple preliminary treatment if presented which aims primarily to analyze the growth rate data within one growth “branch,” i.e., for a regime in which crystal thickness is approximately constant. Under these conditions the growth rate is approximately linear with crystallization temperature, as expected for rough growth surfaces, but not for smooth (faceted) ones. Simulation results are included which are in agreement with a simple equation and with experiment. The analysis enables the growth rates for different branches to be compared in a systematic way. A very steep decrease in growth rate with increasing crystal thickness is clearly illustrated, together with some influence of molecular weight. The general trend for chain folding can be seen as a consequence of this steep decrease. Parallel work on systems in which crystal thicknesses vary continuously with crystallization temperature led to the realization that “rounding off” will occur at the crystal perimeter and that this will give rise to an entropic barrier for the crystal advance. This argument is presented in the context of extended-chain and once-folded crystallization, from which it is clear that growth rates should be much lower as crystal thicknesses increase, and for folded-chain as compared with extended-chain crystals. Different morphologies are interpreted in terms of changes in surface structure which are probably due to kinetic as well as equilibrium effects.     

AFM-tip-induced crystallization of poly(ethylene oxide) melt droplets

The AFM-tip-induced crystallization of poly(ethylene oxide) (PEO) melt droplets was studied. The melt droplets with a height of 50–100 nm and a lateral size of 2–3 μm were obtained by melting the PEO ultra-thin films on a mica surface. For the PEO samples with average molecular weights (M _n) ranging from 1.0 × 10³ g/mol to 1.0 × 10⁴ g/mol, the lateral perturbation from the AFM tip in the hard-tapping or nanoscratch modes could not induce the growth of the flat-on lamellae. In contrast, under AFM nanoindentation mode, the tip-induced crystallization occurred when a sufficiently high vertical tip force was applied to the melt droplets of PEO with M _n ⩾ 1.0 × 10⁴ g/mol. Moreover, the experimental results indicated that the AFM-tip-induced crystallization of PEO in the nanoindentation process had molecular weight dependence. Translated from Acta Polymerica Sinica, 2006, (4): 553–556 (in Chinese)     

Nd:Na3La9O3(BO3)8晶体生长和性质研究

采用顶部籽晶法生长出掺杂浓度为3％的Nd：Na3La9O3（B03）8（Nd：NLBO）晶体。X射线粉末衍射图表明Nd：NLBO与NLBO的晶体结构相同，属于六方晶系。Nd：NLBO（3％）晶体的分凝系数为1．05。测试了晶体的吸收光谱，Nd：NLBO晶体在804nm有较强的吸收，吸收截面为3．2×10^20cm^2，半宽度为6．3nm。Nd：NLBO可能是一种潜在的自倍频晶体。     

Transfer hydrogenation processes to mu(3)-alkylidyne groups on the organotitanium oxide [Ti(3)Cp*O(3)

The photochemical treatment of mu(3)-alkylidyne complexes [[TiCp*(mu-O)](3)(mu(3)-CR)] (R=H (1), Me (2), Cp*=eta(5)-C(5)Me(5)) with the amines (2,6-Me(2)C(6)H(3))NH(2), Et(2)NH, and Ph(2)NH and the imine Ph(2)C=NH leads to the partial hydrogenation of the alkylidyne moiety that is supported on the organometallic oxide, [Ti(3)Cp*O(3)], and the formation of new oxoderivatives [[TiCp*(3)(mu-CHR)(R'NR")] (R"=2,6-Me(2)C(6)H(3), R'=H, R=H (3), Me (4); R'=R"=Et, R=H (5), Me (6); R'=R"=Ph, R=H (7), Me (8)) and [[TiCp*(mu-O)](3)(mu-CHR)(N=CPh(2))] (R=H (9), R=Me (10)), respectively. A sequential transfer hydrogenation process occurs when complex 1 is treated with tBuNH(2), which initially gives the mu-methylene [[TiCp*(mu-O)](3)(mu-CH(2))(HNtBu)] (11) complex and finally, the alkyl derivative [[TiCp*(mu-O)](3)(mu-NtBu)Me] (12). Furthermore, irradiation of solutions of the mu(3)-alkylidyne complexes 1 or 2 in the presence of diamines o-C(6)H(4)(NH(2))(2) and H(2)NCH(2)CH(2)NH(2) (en) affords [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(6)H(4)NH)] (13) and [[TiCp*(mu-O)](3)(mu(3)-eta(2)-NC(2)H(4)NH)] (14) by either methane or ethane elimination, respectively. In the reaction of 1 with en, an intermediate complex [[TiCp*(mu-O)](3)(mu-CH(2))(NHCH(2)CH(2)NH(2))] (15) is detected by (1)H NMR spectroscopy. Thermal treatment of the complexes 4-10 quantitatively regenerates the starting mu(3)-alkylidyne compounds and the amine R'(2)NH or the imine Ph(2)C=NH; however, heating of solutions of 3 or 4 in [D(6)]benzene or a equimolecular mixture of both at 170 degrees C produces methane, ethane, or both, and the complex [[TiCp*(mu-O)](3)[mu(3)-eta(2)-NC(6)H(3)(Me)CH(2)]] (16). The molecular structure of 8 has been established by single-crystal X-ray analysis.     

On the structure and chemical bonding of tri-tungsten oxide clusters W3On- and W3On (n=7-10): W3O8 as a potential molecular model for O-deficient defect sites in tungsten oxides

Electronic and structural properties of a series of tri-tungsten oxide clusters, W3On- and W3On (n=7-10), are investigated using photoelectron spectroscopy and density functional theory (DFT) calculations. Both W 5d and O 2p detachment features are observed for n=7-9, whereas only detachment features from O 2p-type orbitals are observed for W3O10- at high electron binding energies (>7 eV). A large energy gap (approximately 3.4 eV) is observed for the stoichiometric W3O9 cluster, which already reaches the bulk value, suggesting that W3O9 can be viewed as the smallest molecular model for bulk WO3. DFT calculations are carried out to locate the most stable structures for both the anion and neutral clusters; time-dependent DFT method is used to predict the vertical detachment energies and to compare with the experimental data. It is shown that W3O9 possesses a D3h structure, in which each W atom is tetrahedrally coordinated with two bridging O atoms and two terminal O atoms. W3O8 and W3O7 can be viewed as removing one and two terminal O atoms from W3O9, respectively, whereas W3O1) can be viewed as replacing a terminal O in W3O9 by a peroxo O2 unit. We show that W3O8 contains a localized W4+ site, which can readily react with O2 to form the W3O10 clusters with a calculated O2 adsorption energy of -78 kcal/mol. It is suggested that the W3O8 cluster can be viewed as a molecular model for O-deficient site in tungsten oxides.     

混合电解质中HCl热力学性质——HCl-C3H8O3-NaCl-H2O体系

活度系数;电动势;电极电势;无液接电池;混合电解质中HCl热力学性质——HCl-C3H8O3-NaCl-H2O体系     

Synthesis and Structure of the First Protonated Zincoborophosphate: (H_3O)Zn(H_2O)_2BP_2O_8·H_2O

IntroductionInthelastfewyearsthesearchfornewmaterialswithmicroporousandzeolite analogoussystemshasprimarilyfocusedonaluminumphosphatesandaluminosilicatecom poundssubstitutedwithavarietyofatoms .1 3 Cobalt sub stitutedaluminophosphatesaresystematicallystudiedmainlyduetotheirpotentialuseassolid acidcatalysts .Insuchmaterials ,theBr nstedacidsiteisgeneratedbyeachsubstitutionofAl(III)byCo(II)inwhichaprotonisneededtobalancethecharge .4 7Tofindnewtypeofze oliticmaterials ,theborophosphatemateri…     

Trace metal assay of U(3)O(8) powder by electrothermal AAS

Methods have been developed for the direct determination of Ag, Ca, K., Li, Mg, Na, Pb, Sn and Zn in U(3)O(8) powder samples by electrothermal AAS. Nanogram and lower amounts of these elements have been determined with a relative standard deviation of 6-16% in mg amounts of sample (either alone or mixed with an equal weight of graphite). The results for NBL reference samples were in reasonable agreement with the certified values. X-Ray diffraction studies on the residues left from the graphite mixtures after the atomization cycle, confirmed the formation of uranium carbide (UC(2)).